1. Field of the Invention
The present invention relates to a liquid-jet head in which a part of a pressure generating chamber, which communicates with a nozzle orifice for ejecting liquid droplets, is constituted by a vibration plate, a piezoelectric element formed on a surface of the vibration plate, and the liquid droplets ejected by a displacement of the piezoelectric element. The present invention also relates to a Liquid-jet apparatus.
2. Related Background of the Invention
As a Liquid-jet apparatus, for example, there has been an ink jet recording apparatus which applies ejection energy to ink in a pressure generating chamber communicating with a nozzle corresponding to a printing signal and ejects ink droplets from a nozzle orifice. An ink jet recording head installed in this ink jet recording apparatus is roughly divided into two types. One is an ink jet recording head in which a heat generating element such as a resistance wire that generates Joule heat by a driving signal is provided in a pressure generating chamber, and ink droplets are ejected from a nozzle orifice by bubbles generated by the heat generating element. The other is a piezoelectric vibration type ink jet recording head in which a part of a pressure generating chamber is constituted by a vibration plate, and ink droplets are ejected from a nozzle orifice by deforming the vibration plate by use of a piezoelectric element.
For the piezoelectric vibration type ink jet recording head, two types have been put into practical use. One is an ink jet recording head which uses a piezoelectric actuator in a long vibration mode, which stretches and contracts a piezoelectric element in its axis direction, and the other is an ink jet recording head which uses a piezoelectric actuator in a flexible vibration mode.
The former is capable of varying a volume of the pressure generating chamber by allowing an end plane of the piezoelectric element to contact the vibration plate and of being manufactured so as to be suitable for high density printing. However, a difficult process, in which the piezoelectric element is split into pieces in a comb teeth shape to make them coincide with an array pitch of the nozzle orifices, and the operation of positioning and fixing the split piezoelectric element onto the pressure generating chamber are required, thus there is a problem of a complicated manufacturing process.
On the other hand, in the latter ink jet recording head, the piezoelectric element can be fabricated and installed on the vibration plate by a relatively simple process, in which a green sheet as a piezoelectric material is adhered while fitting a shape thereof to the shape of the pressure generating chamber and is sintered. However, a certain size of the vibration plate is required due to the use of flexible vibrations, thus there is a problem that a high density array of the piezoelectric elements is difficult.
Meanwhile, in order to solve such a disadvantage of the latter recording head, as disclosed in Japanese Patent Laid-Open Publication No. Hei 5(1993)-286131, a recording head is proposed, in which an even piezoelectric material layer is formed over the entire surface of the vibration plate by a film deposition technology, the piezoelectric material layer is split into a shape corresponding to the pressure generating chamber by a lithography method, and the piezoelectric element is formed so as to be independent for each pressure generating chamber. According to this gazette, the operation of adhering the piezoelectric element onto the vibration plate is not required, and thus there is an advantage that not only the piezoelectric element can be fabricated and installed by accurate and simple technique called a lithography method, but also the thickness of the piezoelectric element can be thinned and a high-speed drive thereof is enabled.
Although it is possible to improve printing quality and printing speed by using the piezoelectric element formed by such a thin film, a further increase in the printing quality and the printing speed has been recently desired.
Such a piezoelectric element is generally driven by a driving IC, and this driving IC is installed on an ink jet recording head. For example, a joint plate where a piezoelectric element holding portion for defining a space having a size which does not disturb a movement of the piezoelectric element is provided is joined to a plane of a passage-forming substrate on the piezoelectric element side, where the pressure generating chamber is formed. A wiring pattern to which an external wiring such as FPC is connected is provided on an upper portion of the joint plate, and the driving IC is fixed thereto.
In the above-described conventional ink jet recording head, since the driving IC and the wiring pattern on the joint plate are electrically connected via a bonding wire in a plurality of spots on one side of the driving IC in a short direction thereof, there is a problem that a comparatively wide space for connecting the boding wire to the joint plate is required and the head becomes large-sized.
On the other hand, although it is possible to meet a demand for improvements of the printing quality and the printing speed by increasing the number of arrays of the nozzle orifices, there is a problem that the driving IC for driving the piezoelectric element must be made large-sized with the increase of the number of the arrays of the nozzle orifices. There is also a problem that when the driving IC is formed to be relatively large-sized, cost significantly increases. Furthermore, when it is intended to make the driving IC large-sized, a voltage drop and the like may occur, and a relatively large wiring area must be secured to prevent the occurrence of the voltage drop and the like. Accordingly, there is a problem that the driving IC is made larger-sized than necessary. Furthermore, it is difficult to form the driving IC so as to have a longer dimension than a certain length, and it may be impossible to cope with the increase of the number of the arrays of the nozzles.
Such problems exist not only in the ink jet recording head which ejects ink but also in other liquid-jet heads which eject liquid other than the ink.